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Abstract

A feedback error signal from a transformer secondary winding is coupled to a control circuit for the primary winding with electrical isolation by a light-emitting diode and a responsive phototransistor.

Country

United States

Language

English (United States)

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Power Supply with Optical Isolator

A feedback error signal from a transformer secondary winding is coupled to
a control circuit for the primary winding with electrical isolation by a light-emitting
diode and a responsive phototransistor.

The AC input, rectified and filtered by 10, is applied to primary winding 15 of
transformer 20. The load voltage VL, taken from secondary winding 25 and
rectified and filtered by 30, is compared by comparator 50 with a stable reference
voltage provided by winding 35, rectifier and filter 40, and reference 45. The
output of 50 drives light-emitting diode 55. Phototransistor 60 is responsive to
the light emitted by 55 and provides a current drive for transimpedance amplifier 65. The current of 55 ranges from I1 to I2 during the regulation cycle and the
voltage output from 65 ranges from V1 to V2.

The signal from 65 and a linear ramp generated by 70 are applied to
modulator 75. The ripple DC voltage across primary winding 15 is modulated as
the modulated pulse from 75 switches power transistor 80.